In the drilling of a well bore for the production of oil from subterranean oil-bearing formations, zones of high permeability which are useful in subsequent production operations are often penetrated. Because completion work involving the cementing of a casing to the well bore can result in the cement entering the permeable formation and acting as a barrier to optimum oil flow, it is desirable to protect the formation against the entry of the cement.
Although it is known to use cement or gels to protect or seal certain formations during treatment of a well, as in fracturing operations or testing other formations, the same techniques are not readily adaptable for sealing off permeable zones during the drilling of a well. A method of protecting a permeable formation which is quick, reliable and effective, and wherein the sealing means can be readily removed at a later time would be highly desirable.